According to The Third Generation Partnership Project (3GPP) Technical Specification Group Radio Access Network, Requirements for Further Advancements for E-UTRA (LTE-Advanced or LTE-A), Release-10 (3GPP TR 36.913 V8.0.0 (2008-06)), which is incorporated herein by reference, LTE-Advanced networks should target a downlink (DL) peak data rate of 1 Gbps and an uplink (UL) peak data rate of 500 Mbps. Comparing Release-8 (LTE) to Release-10 (LTE-Advanced), the UL peak data rate has increased from 50 Mbps to 500 Mbps, and the peak downlink (DL) rate has increased up to 1 Gpbs.
One important aspect of LTE-Advanced is the advanced topology network it is intended to provide—heterogeneous networks with a mix of large cells (macro) with small cells (pico, femto, remote radioheads) and relay nodes. As compared to LTE, LTE-A provides the addition of many smaller and lower power nodes or cells and improves capacity and coverage. In order to provide the improved data rates, LTE-Advanced introduces “multicarrier” which refers to the aggregation of multiple carriers to increase data rates and provide more bandwidth for a user device/equipment (UE).
A further enhancement, known as coordinated multiple point transmission/reception (CoMP), may be considered in a future release of LTE, for example Release-11, Release-12 or beyond. With CoMP, a UE can transmit or receive signals from multiple points jointly, where multiple points may be multiple cells or multiple sites, even multiple antennas.
In LTE or LTE-A compliant systems, there exist multiple component carriers for carrier aggregation. In LTE Release-10, each component carrier (CC) is a Release-8 compatible component carrier. In other words, a Release-8 UE has the functionality to transmit and receive data over each component carrier. Hence for each Release-8 compatible component carrier, there are multiple physical/transport channels for each CC in the downlink, including: Physical broadcast channel (PBCH) carrying the broadcast channel (PCH), Physical downlink shared channel (PDSCH) carrying the down-link shared channel (DL-SCH) and paging channel (PCH), Physical multicast channel (PMCH) carrying the multicast channel (MCH), Physical downlink control channel (PDCCH) carrying DCI information, Physical control format indicator channel (PCFICH) carrying HI information, and Physical hybrid ARQ indicator channel (PHICH) carrying CFI information. In addition, there are numerous reference and synchronization signals for each CC in the downlink, including: common reference signal (CRS), channel state information reference signal or channel status indicator reference signal (CSI-RS), positioning reference signal (PRS), demodulation reference signal (DM-RS), primary synchronization signal and secondary synchronization signal, as specified in 3GPP Release-8 specifications, for example, 3GPP TS 36.211, 36.212, 36.213. etc.
In Release-8 and Release-10, the CRS signal is a reference signal that enables the UE to perform channel estimation for demodulation of the PDCCH and other common channels, as well as for measurement and feedback. In Release-10, the CSI-RS signal is introduced and used for Release-10 UEs to measure the channel status, especially for multiple antennas cases. In addition, other feedback information may be based on the measurement of CSI-RS, such as a precoding matrix indicator (PMI), a channel quality indicator (CQI), and a rank indicator (RI) of the precoding matrix. The CSI-RS signals (in Release-10) can support up to eight (8) transmission antennas while the CRS signals (Release-8/9) can only support a maximum of four (4) transmission antennas. The number of CSI-RS antenna ports can be 1, 2, 4 and 8. While supporting the same number of antenna ports as the CRS signal, the CSI-RS signal uses much less overhead due to its low density in time and frequency. The CSI-RS signal pattern is transmitted to the UE using a radio resource controller (RRC) signal and can support up to 8 transmission antennas. The CSI-RS signal is transmitted repeatedly/periodically with a subframe offset.
To reduce the interference caused by the CSI-RS signals of neighbor cells, muting is performed on the PDSCH transmission. In other words, the PDSCH transmission should ideally transmit nothing in the muted resource elements indicated by the muting pattern. Since there is signaling that informs a Release-10 UE of the muting pattern, the UE can discard the muted resource elements in the reception of PDSCH.
The muting pattern is signaled to the UE using a 16-bit bitmap. Each bit represents a 4-port CSI-RS pattern. Bit 1 indicates the 4-port CSI-RS pattern is muted, and bit 0 indicates the 4-port CSI-RS pattern is not muted.
In general terms, orthogonal frequency-division multiple access (OFDMA) provides for the division of frequency bandwidth into multiple subcarriers in the frequency domain. In the time domain, one subframe is divided into multiple OFDM symbols. Each OFDM symbol may have a cyclic prefix to avoid or reduce inter-symbol interference resulting from multiple path delay. One resource element is defined by the time-frequency resource within one subcarrier and one OFDM symbol. Reference signals and other signals such as the data channel (PDSCH) and control channel (PDCCH) are orthogonal and multiplexed in different resource elements in the time-frequency domain. The signals are modulated and mapped into resource elements (an inverse Fourier transform per each OFDM symbol transforms signals in the frequency domain into signals in time domain).
When carrier aggregation is utilized, the UE and eNodeB communicate using two or more component carriers (CC). Each component carrier is also referred to as a “cell.” For purposes of reference, the term Primary Cell (PCell) includes the cell operating in the primary frequency (component carrier) in which the UE either performs the initial connection establishment procedure or initiates the connection re-establishment procedure, or the cell indicated as the primary cell in a handover procedure. The term Secondary Cell (SCell) includes the cell operating on a secondary frequency (component carrier) which may be configured once a PCell with the UE is established and which may be used to provide additional radio resources.
Once established, the Pcell connection may be used to signal system information and cell ID information to the UE for setup of an Scell. In a heterogeneous-type network, this Scell may be interfered with by other cells resulting in a failure of the UE to detect the Scell's synchronization signals. The Pcell may signal the UE that the synchronization information (and cyclic prefix information) of the Pcell can also be used for the Scell.
However, this previous system design assumes a physical broadcast channel (PBCH), synchronization signals (SCH), and/or CRS signals (CRS) are always broadcast on the secondary component carrier.